Dissipative epoch

Figure 18 Schematic of epochs for a chemical reaction in solution. E represents the equilibrium epochs, G-D represents the generative-dissipative epochs, I represents the intrinsic or gas-phase epochs, and R represents the recrossing epoch. Adapted from ref. 215.

Benjamin and Wilson discuss many more features of this ICN photodissociation than we have space to summarize. Throughout their work is a theme which we previously discussed there is a timescale in the solution phase dynamics during which there is little deviation from what is observed in the gas phase. In this system, the rapidity with which the choice of final state is made gives an extra importance to this gas phase epoch. Furthermore, as Benjamin and Wilson stress, there are close parallels between photodissociation processes, which are more easily studied experimentally, and the thermally activated process in that gas-phase like periods as well as periods of dissipation of energy back to the solvent occur in both, and also that the time inverse of photodissociation can be compared approximately with the barrier climbing of the reactants in a thermally activated process. 

We wish to make two points about epochs before going on to a discussion of specific systems. First, the picture that we have presented is one where the reactive trajectories arise out of equilibrium, climb the reaction barrier, and then go on to a product equilibrium state. This picture clearly does not hold for nonequilibrium processes such as the photodissociation systems we have discussed. However, the return of these systems to equilibrium often shows the same intrinsic, dissipative, and equilibrium epochs as in equilibrium reaction systems. Thus, one may be able to identify epochs in photodissociation dynamics as well, as has been already discussed in conjunction with the simulation of ICN photodissociation in rare gas solution. ... 

Much attention has been paid recently to an apparent excess of faint blue galaxies observed in photometric surveys. When the models of the B band number counts are normalized at B=16, the data show an excess over the luminosity evolution models of a factor of 2 at B=22. ([Tyson, 1988], [Lilly et al., 1991]) However, the K band number counts do not show this same excess, ([Gardner et al., 1993]). The shape of the number-redshifr distribution of surveys conducted at 20 < B < 22.5 by [Broadhurst et al., 1988] and [CoUess et al., 1990] are fitted by the no-evolution model. The median redshifts of the data from these surveys, and deeper data of [Cowie et al., 1991] and [AUington-Smith et al., 1992] show no evolution as faint as B=24. Proposed explanations for the high B band number counts include massive amounts of merging at intermediate redshifts (z 0.4) ([Broadhurst et al., 1992]) and an excess population of dwarf galaxies which appears at these redshifts, but has dissipated or faded by the present epoch. ([Cowie et al., 1991])... 

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